Navigation system and method

Abstract

In a global positioning system (GPS), such as the NAVSTAR/GPS system, wherein the position coordinates of user terminals (14) are obtained by processing multiple signals transmitted by a constellation of orbiting satellites (16), an acquisition-aiding signal generated by an earth-based control station (12) is relayed to user terminals via a geostationary satellite (10) to simplify user equipment. The aiding signal is FSK modulated on a reference channel slightly offset from the standard GPS channel. The aiding signal identifies satellites in view having best geometry and includes Doppler prediction data as well as GPS satellite coordinates and identification data associated with user terminals within an area being served by the control station (12) and relay satellite (10). The aiding signal significantly reduces user equipment by simplifying spread spectrum signal demodulation and reducing data processing functions previously carried out at the user terminals (14).

We claim: 
     
       1. A system for determining the position of a user terminal comprising: means remote from said user terminal for transmitting a signal containing information indicative of the location of the signal transmitting means, almanac data, timing and synchronization data (epoch) and clock correction data; and   means remote from said signal transmitting means and said user terminal for receiving said transmitted signal and converting said transmitted signal to an aiding signal containing information which identifies said signal transmitting means as well as the spatial coordinate data and predicted Doppler data for said signal transmitting means, said receiving means transmitting said aiding signal to said user terminal;   said signal transmitting means also transmitting said signal to said user terminal.   
     
     
       2. The system of claim 1 wherein said signal transmitting means includes a plurality of signal sources which are displaced from each other. 
     
     
       3. The system of claim 2 wherein said plurality of signal sources are a constellation of satellites. 
     
     
       4. The system of claim 1 wherein said aiding signal is transmitted with frequency shift key (FSK) modulation. 
     
     
       5. The system of claim 1 wherein said aiding signal is transmitted to said user terminal via a relay tower. 
     
     
       6. The system of claim 1 wherein said aiding signal is transmitted to said user terminal via a relay satellite. 
     
     
       7. The system of claim 1 wherein said aiding signal includes a stepped pseudo-random (PRN) code reference. 
     
     
       8. The system of claim 1 wherein said user terminal includes a receiver with a pseudo-random (PRN) code generator. 
     
     
       9. A method for determining the position of a user terminal comprising: transmitting a signal containing information indicative of the location of the signal source, almanac data, timing and synchronization data (epoch) and clock correction data;   receiving said signal at said user terminal;   receiving said signal at a location remote from said signal source which is also remote from said user terminal;   converting said signal at said remote location to an aiding signal containing information which identifies said signal source as well as the predicted Doppler data and the spatial coordinate data for said signal source;   transmitting said aiding signal to said user terminal.   
     
     
       10. The method of claim 9 wherein said transmitted signal consists of a plurality of signals originating from displaced sources. 
     
     
       11. The method of claim 10 wherein said displaced sources are a constellation of satellites. 
     
     
       12. The method of claim 9 wherein said aiding signal is transmitted with frequency shift key (FSK) modulation. 
     
     
       13. The method of claim 9 wherein said aiding signal is transmitted to said user terminal via a relay tower. 
     
     
       14. The method of claim 9 wherein said aiding signal is transmitted to said user terminal via a relay satellite. 
     
     
       15. The method of claim 9 wherein said aiding signal includes a stepped pseudo-random (PRN) code reference. 
     
     
       16. The method of claim 9 wherein said user terminal includes a receiver with a pseudo-random (PRN) code generator. 
     
     
       17. In a system for determining the position of a user terminal including: (1) means remote from said user terminal for transmitting a signal containing information indicative of the location of the signal transmitting means, almanac data, timing and synchronization data (epoch) and clock correction data; and   (2) receiving means at said user terminal for receiving said transmitted signal:   the improvement in said system comprising: (1) means remote from said signal transmitting means and said user terminal for receiving said transmitted signal and converting said transmitted signal to an aiding signal containing information which identifies said signal transmitting means as well as the predicted Doppler data and the spatial coordinate data for said signal transmitting means; and   (2) means for transmitting said aiding signal to said user terminal;   whereby the complexity of said receiving means may be relaxed.     
     
     
       18. The system of claim 17 wherein said signal transmitting means includes a plurality of signal sources which are displaced from each other. 
     
     
       19. The system of claim 18 wherein said plurality of signal sources are a constellation of satellites. 
     
     
       20. The system of claim 17 wherein said aiding signal is transmitted with frequency shift key (FSK) modulation. 
     
     
       21. The system of claim 17 wherein said aiding signal is transmitted to said user terminal via a relay tower. 
     
     
       22. The system of claim 17 wherein said aiding signal is transmitted to said user terminal via a relay satellite. 
     
     
       23. The system of claim 17 wherein said aiding signal includes a stepped pseudo-random (PRN) code reference. 
     
     
       24. The system of claim 17 wherein said user terminal includes a receiver with a pseudo-random (PRN) code generator.